In modern wireless communications, most wireless networks operate on a particular licensed or unlicensed wireless frequency. Different types of wireless communications, such as cellular communications, paging communications, amateur radio communications, and so on, have different frequency spectra assigned as standard frequencies for electronic devices employing these types of communications. Different states or national governments might modify these frequencies within their jurisdictions to some extent, but generally the frequency employed for a given wireless system, IEEE 802.11 local area networks for instance, will be the same worldwide.
As some modes of wireless communications have become increasingly popular, their associated frequency spectra have become increasingly crowded. As an example, the frequency spectrum generally employed by cellular telephone communications is far more crowded than that employed by amateur radio, due to the relative popularities of these two forms of wireless communication. As a result, some frequency spectra become highly congested, whereas others are relatively free. This imbalance in utilization of various frequency spectra has lead to a very inefficient use of the overall radio frequency spectrum.
Cognitive radio was first proposed as a mechanism for providing a more intelligent and adaptive paradigm for wireless communication. This mechanism looked to leverage the relatively ubiquitous smart-phone type mobile communication devices having sophisticated software logic to accomplish adaptive and dynamic wireless communications. Initial proposals for cognitive radio envisioned computer to computer communications sufficiently refined to detect user communication needs as a function of use context, and deliver radio resources or wireless services configured particularly for those needs. This model could theoretically result in a software-defined radio platform that could eventually evolve into a fully reconfigurable wireless system that adapts its communication variables in response to network and user demands.
Although many conceptual proposals for cognitive radio are yet to achieve any realization, those addressing frequency spectra utilization have already been initiated. This is largely because the inefficient use of radio frequencies has become such an immediate and multi-faceted problem. For instance, fixed spectrum allocation for systems like cellular networks, prevent rarely used frequencies (e.g., assigned to specific services) from being used by unlicensed users. This is so even where additional transmissions on those frequencies would not interfere with the assigned service.
One of the first applications of cognitive radio, therefore, has been to avoid potential collisions on licensed or otherwise pre-allocated frequency spectra. Thus, cognitive radio systems have been developed to sense legitimate user presence on a given spectrum and avoid utilizing that spectrum in a manner that would cause a collision. When no user presence is detected, the cognitive radio system would utilize the spectrum to a greater degree, or without restraint. This can be accomplished by active monitoring of several factors in the external and internal radio environment, including radio frequency spectrum, user behavior and network state.
One existing problem in spectrum sensing cognitive radio is designing high quality spectrum sensing equipment cost effectively enough for mass production for the handheld electronic communication device market. Another problem is designing algorithms for exchanging spectrum sensing data between nodes. Simple energy detectors may not be sufficiently accurate to guarantee detection of other users in a given spectrum, suggesting a need for more sophisticated spectrum sensing techniques, or for increasing a number of cooperative sensing nodes to decrease false detection rates, and sharing cooperative measurements more effectively. Therefore, a need exists for more sophisticated mechanisms to accurately sense the presence of other users on wireless frequencies, and to apply that sensing toward efficient utilization of those wireless frequencies.